1. Field of the Invention
The present invention relates to a multi-lens imaging apparatus and, more particularly, to a multi-lens imaging apparatus which obtains a single high-fine image by synthesizing a plurality of images obtained by picking up a common object image using a plurality of imaging systems and to an apparatus which can provide a image having a different aspect ratio from that of a image obtained by a single imaging apparatus, for example, a panoramic image, by synthesizing a plurality of images obtained using a plurality of imaging optical systems.
2. Related Art
When an ultra high-fine image consisting of 4,000.times.4,000 pixels is picked up by an imaging system, and the picked-up image is displayed on an ultra high-fine monitor, problems associated with techniques for achieving a high density and a high sensitivity in the imaging system are posed. As a method of solving such problems in the imaging system, the principle of a multi-lens imaging apparatus for picking up an image of a common object using two imaging systems each having a small number of pixels, and obtaining a single high-fine image by synthesizing the two images obtained by the two imaging systems has been proposed. In the multi-lens imaging apparatus based on this principle, as shown in FIG. 1, right and left side imaging systems 110.sub.R and 110.sub.L are prepared, and pick up an image of an object 101 by shifting their sampling points by a 1/2 spatial phase pitch. A right side image I.sub.R obtained by the right side imaging system 110.sub.R and a left side image I.sub.L obtained by the left side imaging system 110.sub.L are synthesized by a microprocessor (to be referred to as a "CPU" hereinafter) 120, thereby obtaining a single high-fine output image I.sub.OUT as compared to a image obtained when the image of the object 101 is picked up by a single imaging system.
FIG. 2 is an explanatory view for explaining a basic arrangement of the right and left side imaging systems 110.sub.R and 110.sub.L shown in FIG. 1.
The left side imaging system 110.sub.L is constituted by a left side imaging optical system 111.sub.L and a left side image sensor 112.sub.L, and the right side imaging system 110.sub.R is constituted by a right side imaging optical system 111.sub.R and a right side image sensor 112.sub.R. The right and left side imaging optical systems 111.sub.R and 111.sub.L have equivalent specifications, and each comprises a zoom lens. The right and left side image sensors 112.sub.R and 112.sub.L have equivalent specifications, and each comprises a camera tube such as a saticon or a solid-state imaging element such as a CCD. Optical axes L.sub.R and L.sub.L of the right and left imaging systems 110.sub.R and 110.sub.L cross almost at a point O on an object surface 102, and these systems are arranged at positions axially symmetrical about a normal O-O' to the object surface 102. When the angle formed between each of the optical axes L.sub.R and L.sub.L and the normal O-O' to the object surface 102 (to be referred to as an "inclination angle" hereinafter) is represented by .theta., 2.theta. is defined as the convergence angle.
In the multi-lens imaging apparatus, when the object distance is changed, the convergence angle 2.theta. is changed by rotating each of the right and left side imaging systems 110.sub.R and 110.sub.L about an X mark shown in FIG. 2 in accordance with the change in object distance, thus performing an imaging operation.
However, in the above-mentioned multi-lens imaging apparatus, only the principle shown in FIG. 1 and the results of principle experiments for demonstrating the principle are presented, and no detailed arrangement of the multi-lens imaging apparatus is presented. Thus, a problem associated with how to arrange the detailed multi-lens imaging apparatus utilizing the above-mentioned principle remains unsolved. Since the optical axes L.sub.R and L.sub.L of the right and left side imaging systems 110.sub.R and 110.sub.L are inclined with respect to the object surface 102, the right and left side images I.sub.R and I.sub.L obtained by the right and left side image sensors 112.sub.R and 112.sub.L suffer from trapezoidal distortions (to be referred to as "keystone distortions" hereinafter), as shown in FIG. 3. As a result, when the right and left side images I.sub.R and I.sub.L are merely synthesized, a high-fine image cannot be obtained.
Since the optical systems are arranged to have a convergence angle therebetween in principle, mis-registration between images obtained from the two imaging operation systems may occur. FIG. 4A shows the outline of mis-registration in a multi-lens imaging system. The system shown in FIG. 4A includes imaging optical systems (lenses) 910 and 920, and image sensors 911 and 921. The imaging optical systems 910 and 920 have optical axes 912 and 922, respectively. When an object image is picked up while the optical axes 912 and 922 are inclined through .theta. in the x-z plane with respect to a central axis O-O', an arbitrary object point on an object surface is represented by P. At this time, if image points of the image sensors 911 and 921 with respect to P are respectively represented by R' and L', since R'.noteq.L', mis-registration occurs, and two images with respect to the object point P are formed on a simply added synthesized image 930, as shown in FIG. 4B. As a result, a high-fine image cannot be provided.
Conventionally, as a panoramic imaging apparatus using a plurality of imaging optical systems and designed for dynamic images, for example, Japanese Laid-Open Patent Application No. 63-8641 is known. In an apparatus of this type, in general, the angle formed between the imaging optical systems is set by mechanical adjustment, so that image fields contact each other. However, it is very difficult to strictly register two adjacent images, and the boundary line between the two images normally becomes conspicuous. For the same reason as described above, since it is difficult to re-focus objects having different object distances or to perform zooming of these objects, the above-mentioned apparatus is limited to a cut photographing use in units of scenes.
As a method of changing the aspect ratio of a frame of a television or video signal (e.g., conversion between 4:3 of the NTSC and 16:9 of the HD or ED2), a method of trimming upper and lower portions or right and left portions of the frame is known. In this method, since a picked-up image is partially used, when an image is picked by an NTSC camera using a 4:3 image sensor, and is output onto a 16:9 HD monitor, a total of 25% upper and lower images are lost in addition to the fact that the number of pixels is originally short, thus considerably deteriorating image quality. Conversely, when an image is picked up by a 16:9 HD camera, and is output onto a 4:3 NTSC monitor, no problem associated with image quality is posed, but the horizontal field angle is decreased by 1/3.